Sensors and Robotics Sensors and Robotics MOBI LE ROBOTI CS DAUIN - - PDF document

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Sensors and Robotics Sensors and Robotics MOBI LE ROBOTI CS DAUIN - - PDF document

Aug 06, 2023 18 likes •262 views

Sensors and Robotics Sensors and Robotics MOBI LE ROBOTI CS DAUIN Politecnico di Torino Basilio Bona CY 02CFI C CFI DV CA 01 OBOTI C RO The Mobile Robotics Challenge Objective: perceive, analyze and understand the

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SLIDE 1

CY 02CFI C

MOBI LE ROBOTI CS

CFI DV

Sensors and Robotics

CA – 01

Sensors and Robotics

OBOTI C

Basilio Bona

RO

DAUIN – Politecnico di Torino

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SLIDE 2

The Mobile Robotics Challenge

CY

Objective: perceive, analyze and understand the environment state around the robot

02CFI C

Measurements change due to the dynamical nature

  • f the environment or of some parts; moreover they

ff t d b hi h l l f i / di t b

CFI DV

are affected by a high level of noise/ disturbances Examples:

CA – 01 – Variability of light condition (scene illumination) – Reflexions OBOTI C – Surfaces with high variability of sound/ light absorption/ reflection properties RO – Sensitivity of measurements with respect to robot pose

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SLIDE 3

Encoders They measure the angular position and speed of

CY

They measure the angular position and speed of

  • nboard motors

Odometry: measurements are integrated to give an

02CFI C

y g g estimate of the position or pose Forniscono misure (imprecise) rispetto al riferimento

CFI DV

locale (propriocettori)

CA – 01 OBOTI C RO

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SLIDE 4

Encoders

CY

Light rays

02CFI C

receiver

CFI DV

Transparent slids Light source

CA – 01 OBOTI C

Rotating

RO

Rotating Disk

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SLIDE 5

Encoders

CY

Incremental Absolute

02CFI C CFI DV CA – 01 OBOTI C RO

Zero notch

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SLIDE 6

Encoders

CY 02CFI C

Source Disk Source Disk

CFI DV

Receiver Receiver

CA – 01

Electronics Electronics

OBOTI C

Shaft Shaft

RO

Shaft Shaft

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SLIDE 7

Encoders

CY 02CFI C CFI DV CA – 01 OBOTI C RO

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SLIDE 8

Encoders

CY 02CFI C CFI DV CA – 01 OBOTI C RO

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SLIDE 9

Encoders

CY 02CFI C CFI DV CA – 01 OBOTI C RO

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SLIDE 10

Heading Sensors

CY

Gyroscopes, inclinometers, compasses, gyrocompasses

02CFI C

They measure the horizontal or vertical angle referred to a given direction

CFI DV

Together with speed measurements they provide an estimate of the position

CA – 01

This procedure is also called dead reckoning and is a characteristic of maritime navigation

OBOTI C

characteristic of maritime navigation

RO

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SLIDE 11

Com passes

CY

Known since the ancient times Is based on the Earth magnetic field (absolute

02CFI C

g measurement) Physical methods: mechanical (magnetic needle),

CFI DV

y ( g ), Hall effect, magnetostrictive effect

Piezoelectric resonators have been used as standard clocks in. recent electronics technologies because

  • f their sharp resonance profiles. We propose a magnetic field sensor consisting of a piezoelectric

t d t t i ti ti l It i ifi d th t it F h i

CA – 01

resonator and magnetostrictive magnetic layers. It is verified that its resonance Frequency changes in a magnetic field with sensitivity high enough to detect terrestrial magnetic field. So, it is useful as an electronic com pass that is in great dem and from the mobile telecommunication technology [ I] . The advantage of this sensor is that it can readily be downsized maintaining a high S/ N because it detects an external field through change of the resonance frequency rather than the analogue output as in the

OBOTI C

MI or the flux gate sensors. (Yoshizawa, N. Shimada, Y. )

Limitations

RO – The Earth magnetic field is rather weak – Easily disturbed by near metallic objects – Less used for indoor navigation

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SLIDE 12

Gyroscopes

CY

They provide an absolute measurement, since they maintain the initial orientation with respect to a fixed reference frame

02CFI C

fixed reference frame Mechanical or Optical

CFI DV

Mechanical

– Standard (absolute) CA – 01 – Rated (differential)

Optical

OBOTI C

Optical

– Rated (differential) RO

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SLIDE 13

Mechanical Gyroscopes Concept: inertial properties of a rotor that spins fast:

CY

Concept: inertial properties of a rotor that spins fast: precession phenomenon Angular moment is conserved and keep the wheel

02CFI C

Angular moment is conserved and keep the wheel axis with a constant orientation Negligible torque is transmitted to the external i f h h l i

CFI DV

mounting of the wheel axis Reaction torque is proportional to the rotation speed the inertia and the precession velocity Ω

τ ω Γ

CA – 01

speed , the inertia and the precession velocity

τ Γω = Ω Ω ω Γ

OBOTI C

If the rotation axis is aligned along the N-S meridian, the Earth rotation does not influence the t

RO

measurements If the rotation axis is aligned along the E-O meridian the horizontal axis measures the Earth meridian, the horizontal axis measures the Earth rotation

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SLIDE 14

Mechanical Gyroscopes

CY 02CFI C CFI DV CA – 01 OBOTI C RO

Rotation axis Rotation axis

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SLIDE 15

Differential Gyroscopes Same construction concept but the cardanic

CY

Same construction concept, but the cardanic joints= gimbals are constrained by a torsion spring

– An angular velocity is measured instead of an angle 02CFI C g y g

Other gyroscopes use the Coriolis effect to measure the

  • rientation variation (e.g., Analog Device ADXRS150 and

ADXRS300)

CFI DV

ADXRS300)

CA – 01 OBOTI C RO

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SLIDE 16

Optical gyroscopes

CY

Two monochromatic laser rays are produced and injected into an optical fiber coiled around a

02CFI C

cylinder One ray turns in one sense, the other in the it

CFI DV

  • pposite sense

That ray that turns in the same sense of the rotation covers a shorter path and shows a

CA – 01

rotation, covers a shorter path and shows a higher frequency; the frequency difference between the two rays is proportional to the

OBOTI C

between the two rays is proportional to the cylinder angular speed Solid state sensors; directly integrable on

RO

; y g silicon together with the electronic circuits

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SLIDE 17

Beacons G ide s stems ith kno n

CY

Guide systems with known absolute position. Also known as landmarks

02CFI C

known as landmarks artificial or natural

– Known and used since ancient CFI DV Known and used since ancient times: sun, mountains, capes, bell towers, marine lighthouses CA – 01

Necessary for indoor motion, where GPS is impossible

OBOTI C

impossible Expensive, they require an i f t t

RO

infrastructure Not easy to adapt to varying i t diti environment conditions

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SLIDE 18

GPS

CY 02CFI C CFI DV CA – 01 OBOTI C RO

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SLIDE 19

Distance Sensors

CY

Also known as range sensors, they measure “large” distances

02CFI C

large distances They use the time-of-flight principle

CFI DV

Ultrasonic (sonar) or laser sensor, since the sound or light speed is known

CA – 01

d cT =

OBOTI C

Distance (two ways)

RO

Time measured Wave speed p (sound/electromagnetic)

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SLIDE 20

Distance Sensors

CY

Speed of sound approx 0.3 /

02CFI C

m/ ms Speed of light (in vacuum) 0 3 m/ ns

CFI DV

0.3 m/ ns Rate 106 3

CA – 01

3 m

– 10 ms using sound waves – only 10 ns with a laser sensor OBOTI C

  • nly 10 ns with a laser sensor

– difficult to measure – laser sensor expensive RO

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SLIDE 21

Distance Sensors

CY

The measurements quality depends on

02CFI C – Uncertain arrival time of the reflected wave (laser and sonar) U t i ti f fli ht (l ) CFI DV – Uncertain time-of-flight (laser) – Aperture angle (sonar) CA – 01 – Interaction with surfaces (sonar and laser) – Variability of the speed (sonar) OBOTI C – Possible speed of the source (sonar) RO

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SLIDE 22

Ultrasonic Sensors

  • A package of sound (pressure) waves is generate and emitted

CY

  • A package of sound (pressure) waves is generate and emitted

the so called chirp

  • Relation is simply:

02CFI C Relation is simply:

cT d =

CFI DV

2

  • The sound speed in air is give as

CA – 01 The sound speed in air is give as

c RK γ =

OBOTI C

specific heat constant R γ γ =

RO

gas constant temperature in Kelvin R K = = p

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SLIDE 23

Ultrasonic Sensors

CY 02CFI C CFI DV CA – 01 OBOTI C RO

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SLIDE 24

Ultrasonic Sensors Used frequencies 40 200 kHz

CY

Used frequencies 40-200 kHz Generated from a piezoelectric source Transmitter and receiver may be separated or not

02CFI C

Transmitter and receiver may be separated or not Sound is emitted in a conic shape A t l 20 40 d

CFI DV

Aperture angle 20-40 degrees

CA – 01

Density spatial distribution

OBOTI C RO

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